Fluid actuated circuit breaker operating mechanism



FLUID ACTUATED CIRCUIT BREAKER OPERATING MECHANISM Filed Dec. 28, 1955 MM w M W 2 M M T M E J j a m t 0/ Q E N fl 9 a s 4 4 IM\/ MW g .M

L? t? n Pa r Oed O Bn t nWA t e v M .w n d 6 J T R United States PatentFLUID ACTUATED CIRCUIT BREAKER OPERATING MECHANISM John W. Beatty,Lansdowne, and Reed M. Anderson, Glenolden, Pa., assignors to GeneralElectric Company, a corporation of New York Application December 28,1953, Serial No. 400,552

16 Claims. (Cl. 200-82) This invention relates to a fluid actuatedoperating mechanism for an electric circuit breaker, and moreparticularly, to an improved arrangement for effecting ex treme highspeed response of such an operating mecha nism.

The conventional fluid actuated operating mechanism comprises a sourceof high pressure fluid, a fluid motor, and a conduit which interconnectsthese parts and contains a control valve operative to permit highpressure actuating fluid to flow to the motor. Where such a controlvalve and conduit is utilized, there is invariably an undesirable timedelay between the time the control valve is opened and the time thatsufficient pressure is built up within the motor to effect high speedoperation of the motor. This time delay results from the distancethrough which the fluid must flow to actuate the motor and also from thepressure reduction produced by the valve and the intervening conduit.

One approach which has been made toward reducing this undesirable timedelay is illustrated in Bartlett Patent No. 2,290,726, wherein the fluidreservoir and the cylinder of the fluid motor have been integrallyconstructed. Although this integral construction appreciably reduces thedistance between the reservoir and the fluid motor, there still existsbetween the reservoir and the motor, a control valve and orificestructure through which all of the actuating fluid must flow in order tooperate the fluid motor. inherently, such flow through these parts willresult in pressure reduction which tends to lessen the speed of responseof the fluid motor.

It is, therefore, an object or" this invention to provide for a circuitbreaker an improved fluid actuated operating mechanism which is capableof extreme high speed.

It is a further object of this invention to arrange the control valvefor a fluid motor in such a manner that the valve is required to passonly a very small portion of the actuating fluid, Whereas the great bulkof the actuating fluid may flow to the fluid motor piston through asubstantially unrestricted path which is independent of the controlvalve.

It is a further object of this invention to subject the working surfaceof a piston of a fluid motor to high pressure actuating fluid within aminimum period of time after the control valve is opened.

It is a further object of this invention to provide a fluid actuatedoperating mechanism which requires no separate pressure switches toefl'ect automatic circuit breaker opening in response to loss ofpressure.

In accordance with one form of the present invention, there is provided,for operating a circuit breaker, a fluid motor comprising casingstructure and a reciprocable piston mounted within said casing structureand having a first wall portion which cooperates with said casingstructure to define a substantially closed reservoir. This reservoir isnormally filled with high pressure actuating fluid, and said firstportion of the piston wall serves as a pressure confining wall of thereservoir. When the piston is in its initial position, it is urged intoabutment with a seat which is arranged to seal olf a second portion ofthe piston surface from the high pressure gas. This second portion ofthe piston surface communicates with a small pilot chamber in which thefluid pressure is controlled by a pilot valve. Operation of the pilotvalve permits an instantaneous build-up of pressure within the pilotchamber which is effective to initiate movement of the piston away fromits seat so as to permit high pressure fluid from said reservoir to flowrapidly past the piston seat and into effective driving relationshipwith said second portion of the piston.

An additional feature of one form of the present in vention is that thepilot valve for the fluid motor is proportioned so that the pressure ofthe adjacent fluid upon the valve creates a force which cooperates withthe coercive forces produced by a magnetic trip latch of the circuitbreaker to normally hold the pilot valve closed against the bias of aspring. If the system pressure should fall below a safe level, thespring overcomes these opposing forces thereby opening the pilot valveto initiate circuit breaker opening operation of the fluid motor.

Further objects and advantages of our invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize our invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of our invention reference may be had to theaccompanying drawing, the single figure of which is a partiallyschematic view of a circuit breaker comprising a fluid actuatedoperating mechanism constructed in accordance with this invention, thefluid actuated mechanism being shown in cross section.

Referring now to the drawing, we have illustrated our invention inconnection with a circuit breaker comprising a movable contact member 10connected, through an insulated operating rod 10:: to a pivotallymounted actuating lever 11. This lever 11 is movable by the fluid motor12 from the solid-line closed position 13 to the dotted-line openposition 14 thereby to effect opening operation of the circuit breaker.The circuit breaker is shown as of the latched-open, biased-closed type,to which our invention is especially applicable; i. e. upon opening ofthe breaker, a latch 15 engages behind a catch 16 to hold the breaker inopen position against the bias of a closing spring 17 until such time asthe breaker is unlatched, as will be described in greater detailhereinafter.

The fluid motor 12 comprises casing structure 2i) having a reducedtubular portion defining a cylinder 22 in which a main actuating piston23 is reciprocably mounted. When the circuit breaker is in the closedposition shown, the piston is positioned in its uppermost positionwherein its upper working surface 30 abuts in sealing relationshipagainst the downwardly directed annular rib or seat 24. For assuring aneffective seal,

the piston 23 preferably carries an insert ring 25 of yieldable materialwhich abuts in registering relationship against the seat 24. When thepiston is in the position shown, its wall portion 26 which is disposedexternal to the seat 24 cooperates with adjacent portions of casingstructure 20 to form a relatively large reservoir 27 which surrounds thepiston 23. This reservoir 27 communicates, through a conduit 28, with asource, such as the tank 29, of high pressure fluid (preferably air) sothat the reservoir 27 is normally filled with air at the same highpressure as the source. It will be observed that the actuating pistonitself actually constitutes a pressure confining wall of the reservoir27, so that at the instant the piston 23 leaves its seat 24, highpressure air from the reservoir 27 instantaneously flows radiallyinwardly past the seat 24, flooding the piston top wall or workingsurface 30, independently of any control valve, thereby to provide afull unrestricted air pressure behind piston 23 throughout substantiallyits entire opening stroke.

For initiating an opening operation of the actuating piston 23, there isprovided control means comprising a pilot valve 33, which in its closedposition, abuts in sealing relationship against an upwardly directedannular seat 34, which, like the piston seat 24, is formed on a part ofthe casing structure 20. The inner surface of the portion of casingstructure extending between the two seats, together with the lowersurface of the seated valve 33 and the upper surface of piston 23,define a small. minimum-space pilot chamber 35. This pilot chamber isnormally at atmospheric pressure due to the presence of a restrictedbleed passage 36 extending from the chamber to atmosphere. The reservoir27, containing air at full supply pressure communicates freely with asubchamber 27a which surrounds the valve seat 34, so that when the pilotvalve 33 is lifted, high pressure air instantly flows past the seat 34and into the chamber 35. The pilot valve 33, being of-the semi-balancedtype,

is aided in its movement toward fully-open position by the high pressureair acting with piston effect upon its lower surface as the pressurebuilds up in the pilot chamber 35. Since the pilot chamber 35 has a verysmall volume, on the order of, say less than two cubic inches, and sinceall of the exits from chamber 35 are quite restricted, air pressurewithin the pilot chamber 35 builds up to a high value substantiallyinstantaneously. This instantaneous pressure buildup immediately unseatspiston 23, so that air then flows unrestrictedly from reservoir 27rapidly past the large seat 24 thereby to subject the piston 23 to fullsupply pressure, as previously described.

From the foregoing description it will be apparent that the air flowpast pilot valve 33' primarily serves to trigger or initiate movement ofthe main actuating piston 23, and as a result, only a minor portion ofthe actuating air flows from the reservoir past the pilot valve, whereasthe major portion of the actuating air, which feeds directly from thelarge surrounding reservoir 27, flows to the working portion of pistonsurface 39 through a substantially unrestricted path which isindependent of pilot valve 33. As a result, the working surface 30 ofthe. actuating piston is exposed to full supply pressure almostinstantaneously after the pilot valve is opened,

whereby extreme high speed response of the fluid motor is produced.

To further increase the speed of response of the fluid motor, lostmotion has been provided between the actuating piston 23 and the contactoperating linkage. lost motion has been obtained in the illustratedembodiment of the. invention by spacing the lower end of the piston rod52 a slight distance from the actuating lever 11, as shown at 36a. twill be apparent that this lost motion spacing at 36a permits initialmovement of thepiston 23' away from. its seat 24 without restraint fromthe operating linkage and the closing spring 17. As a result, only acomparatively small pressure buildup within the pilot chamber 35 isneeded in order to initiate piston movement. Once piston movement isinitiated, the piston is immediately exposed to full supply pressure, aspointed out hereinabove.

For normally holding the piston 25 inits uppermost or seated positionagainst its seat 24, the seat 24 and the piston 23 are proportioned sothat an upwardly-acting diiferential air pressure is exerted on thepiston when it is seated. Specifically, the. effective piston surfacearea disposed radially inwardly of annular seat 24 is slightly greaterthan the eflective piston surface area bounded by annular piston sealingring 37, and as. a result,,a. greater area is exposed to air pressureforces acting upwardly than to those acting downwardly. In view. of thispressure relationship, the compression spring 33- which is disposedbeneath the piston 23 may be ofv a relatively light construction sinceit serves mainly to This insure that the piston 23 will be properlyseated when the system is being filled with compressed air, eitherinitially or after subsequent exhaustings of the system, as may berequired for maintenance.

For initiating an opening operation of the pilot valve 33 in response topredetermined electrical conditions, there is provided a pilot armaturein the form of alever iti which is centrally pivoted at 41 and which isoperatively interconnected at one end through link 42 to the pilot valve33. This armature lever 40, at its other end, is normally held in ahorizontal position by the attraction of a magnetic latching device 43.Since the details of this magnetic latch form no part of the presentinvention and correspond to a latch 21 described in Coggeshall Patent2,479,315, the latch 43' of the present application is shown onlydiagrammatically. For the purposes of this description, it is believedsufficient merely to point out that the armature lever 40 is normallyheld in its horizontal position by coercive forces produced by apermanentmagnet 43a forming a part of the latch. The latch additionallycomprises a trip coil 43b connected in a control circuit 43c. The tripcoil is arranged in such a manner that when control power is appliedthereto the coercive forces of the permanent magnet 43a are instantlyneutralized so that the armature lever 40 is free to rapidly separatefrom the latch 43 under the bias of trip latch spring 44 acting througha slidab'ly mounted guide element 45. For suitably applying the controlsource of power to the trip coil 43b of latch 43 in response topredetermined electrical conditions, e. g. overcurrent in line 46, thereis provided an overcurrent' relay 47 connected to be energized from acurrent transformer ib. When relay 47 is actuated, its normally-opencontacts 49 are closed to complete a control power circuit through thetrip coil 43b of latch 43, thereby effecting high-speed release ofarmature lever 40 in the desired manner described.

After the main actuating piston 23 has moved downwardly through itscontact opening stroke, it. is desirable to rapidly reset, or return,the operative parts of the fluid motor to the normal position shown inthe drawing, so that the fiuid motor thereby is placed in readiness torespond properly to a subsequent contact reclosing operation of thebreaker. To effect this desired rapid resetting, there is providcd atthe lower side of the fluid motor a cylinder 50 reciprocably receiving areset piston 51, which is interconnected with main actuating piston 23by a piston rod 52. The effective working surface of the reset pistonSlis greater than the effective working surface of piston 23, so thatthe reset piston 51 may predominate. when both working surfaces aresubjected to the high pressure air. For. supplying high pressure air to,the lower side of the return piston 51 at a predetermined instant. afterfull opening of the circuit breaker contacts 10 is assured, there isprovided a duct 53 interconnecting the reservoir 2'7 and the bore ofcylinder 50. Air flow through the duct is controlled by a biased-closedcontrol valve 54. This control valve 54 is opened with a predeterminedshort time delay after opening movement of piston 23 is initiated. Suchtime delay is achieved in one form of the presentinvention by a timedelay reservoir shown schematically. at 55'. This reservoir 55:isconnectedby external piping 56 with the pilot chamber 35 and with acontrol cylinder 57 for a valve operatingpistonSS disposed at thedelivery end of the piping. The flow of air into piping 56 from pilotcharnber 35 is restricted by a bleed passage 56a through which airenters piping 56.

The resetting of the piston may be described as follows: When openingoperation. of piston 23 is initiated by the opening of valve 33, highpressure air also will thereby permitting high pressure air flow fromthe main reservoir 27 to cylinder 50 whereby to return the then loweredreset piston to its upper and reset position.

Resetting of the latch 43 and valve 33 are effected by latch-resettingmotor 60. This motor 60 communicates with the resetting cylinder 50through a motor control duct 61 which conducts high pressure air fromthe cylinder 50 to the motor 60 when the upwardly moving reset pistonhas moved above and uncovered the cylinder side port 62. At this instantthe high pressure gas supplied to the motor 69 will lift piston 63 untilits rod 64 pivots the pilot armature lever 49 from its dotted lineposition to the solid line reset position wherein it is held by magneticlatch 43. This pivoting of armature lever 40 returns the pilot valve 33to its normally-closed, circuit-condition-responsive position. Thepressure beneath the main reset piston 51 is maintained for a sufficientlength of time to permit the pressure in pilot chamber 35 to be relievedto atmosphere through the bleed passage 36, whereby the main actuatingpiston 23 will be held in closed position so long as valve 33 ismaintained closed. Concurrently with this movement of main piston 23into its reset position, the bleed port 63a in cylinder 56 is uncoveredso that pressure beneath piston 51 soon falls to the atmospheric level.When this condition occurs, the fluid motor 12 is completely reset andis in readiness to properly respond to a reclosing operation of thecontacts 11'). That is, in the event that the contacts are reclosed,say, upon a sustained fault, the fluid motor is in readiness toimmediately open the contacts.

in order to prevent initiation of a circuit breaker rapid reclosingoperation before the latch 43 and the motor 12 are safely reset, thereis provided in the closing or reclosing control circuit 70 an interlockmeans 71. This interlock means comprises a switch member 72 which isoperated from the pilot armature lever 40 to bridge contacts 73 when thelatch and motor are reset and which opens the contacts 73 whenever theseparts are tripped or not reset. Contacts 73, circuit breaker closingswitch 74-, and the operating coil 75 for the holdopen latch i arearranged in series relationship in the closing control circuit 70, sothat closing of the switch 74 will be effective to close the circuitbreaker only if the contacts 73 are closed. If the contacts 73 areclosed, closing of the switch 74 will energize coil 75 to unlatch thebreaker and permit contact 19 to close under the influence of spring 17.If the latch and motor have not been reset, the contacts 73 will remainopen thereby preventing energization of latch coil 75 by closing switch74.

Another feature of the present invention, is that the mechanism, withoutthe necessity of any additional pressure switches, is capable ofautomatically opening the circuit breaker in case the supply pressureshould fall below a predetermined operating value, thereby insuring thatthe breaker will not remain closed if the prevailing conditions are notavailable for effecting a fully rated interrupting capacity openingoperation. This automatic feature is obtained by the balanced design ofthe valve 33 and the magnetic trip latch 43. More particularly, whenvalve 33 is closed, the trip latch spring 44 is opposed by the holdingforce of the permanent magnet 43a of magnetic latch 43 and by thedifferential air pressure on valve 33, namely, the preponderating airforce over the larger area bounded by the pilot valve seat 34 minus thelesser air force over the smaller area bounded by the seal 80 whichsurrounds the valve stem. Thus, if the system pressure falls, thispneumatic differential closing force on the valve will declineaccordingly. The spring 44 is designed to provide a force which is justsufficient to overcome the holding force of permanent magnet 43a and thedeclining hold-close force from the pilot valve 33 when the air supplypressure has fallen to some predetermined fraction of its originalvalue. When the pressure does drop to this predetermined fractionalvalue, which corresponds to a diminished, but adequate, operating air'pressure, the spring 44 will overcome the combined pilot valve force andmagnetic latch force whereby to open valve 33 thereby initiating anautomatic opening operation of the circuit breaker while there is stilladequate operating pressure.

For initially filling the system with high pressure air, it is desirableto hold the pilot valve 33 closed so that the system will not lose air,say, through the bleed passage 36 at a rate which materially interfereswith the effective build-up of pressure in the system. To this end, thelift piston 63 of the latch reset motor is provided with a manuallyoperable lift rod 81 which, when raised, resets the latch 43 to itsmagnetically attracted position and lowers the pilot valve 33 to aclosed position, whereby to seal off the top of pilot chamber. Thebottom of the pilot chamber will be sealed off by the piston 23 which,under these no-pressure conditions, is held in its uppermost position bythe light compression spring 38 which, as already explained is providedfor this purpose.

Another feature of this invention which contributes to high speedmovement of the main actuating piston 23 is that no significant amountof high pressure air is permitted to leave the chamber surrounding thepiston until a substantial portion of the opening stroke has beencompleted. Thus, substantially full supply pressure is available duringthis portion of the opening stroke. This essentially closed condition ofthe surrounding chamber results from the fact that the only exit fromthe chamber which is of significant size is blocked by the then closedcontrol valve 54 for a predetermined period of time after the initiationof the piston opening stroke. This time delayed operation of valve 54 isobtained by the use of time delay reservoir 55, as describedhereinabove.

While we have shown and described a particular embodiment of ourinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from ourinvention in its broader aspects and we, therefore, aim in the appendedclaims to cover all such changes and modifications as fall within thetrue spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a circuit breaker operating mechanism, a fluid motor comprisingcasing structure, a piston movable within said casing structure, saidpiston having a Wall portion cooperating with said casing structure todefine a reservoir filled with high pressure fluid, said wall portionforming a pressure confining wall of said reservoir, sealing meansengageable with said piston to seal oil a working portion of the pistonwall from said high pressure fluid in said reservoir, means defining apilot chamber communicating with said sealed-off working portion, andpilot valve means movable to etfect an increase in the fluid pressurewithin said pilot chamber whereby to move said piston out of sealedrelationship with said sealing structure.

2. A fluid motor comprising casing structure, a piston movable withinsaid casing structure, said piston having a first pressure-confiningwall portion cooperating with said casing structure to define a fluidreservoir, sealing means engageable with said piston to seal off asecond portion of the piston wall from fluid in said reservoir, meansdefining a pilot chamber communicating with said second portion, andpilot valve means disposed between said reservoir and said pilot chamberand movable to permit fluid to flow from said reservoir into said pilotchamber whereby to move said piston out of scaled relationship with saidsealing structure.

3. A fluid motor comprising casing structure, a piston movable withinsaid casing structure, said piston having a first wall portioncooperating with said casing structure to define a reservoir filled withhigh pressure fluid, said first wall portion serving as apressure-confining wall of said reservoir, sealing means cooperable withsaid piston to seal 05 a second portion of the piston wall from saidgran ees high pressure fluid, control means including, a pilot valveopenable to apply high pressure fluid to said second portion soas tomove said piston out of scaled relationship withsaid sealing meanswhereby fluid from. said reservoir flows past said sealing means andinto drive transmitting relationship with said second portion of thepiston.

4-. The fluid motor of claim 3 in combination with means for returningsaid piston to itsposition of scaled having a predeterminedcross-sectional area, a movable piston slidably received in sealedrelationship Within said opening, said casing structure and said pistondefining therebetween afluid reservoir, sealing means coopcrable withsaid piston to seal off. a working portion of the piston surface fromfluid within said reservoir, the slicetive area of said sealed-olf-Working portion being larger than said predetermined cross-sectional.area, means dofining a pilot chamber communicating with said sealed-offWorkingportion, and pilot valve means movable to control the fluidpressure within said pilot chamber.

6. A fluid motor comprising a casing, a piston movably mounted withinsaid casing. and having a working surface and a pressure confining wallportion, said pressure confining wall portion. being disposed tocooperate with said casing to define a reservoir containing fluid underpressure, means biasing said piston for movement in one direction, stopmeans on said casing engaging said working surface in sealing relationto limit biasing movement of said piston and to seal atv least a portionof. said working surface from said fluid in said reservoir, and meansincluding a valve movable to admit fluid under pressure to said portionof the working surface thereby to move said piston against its bias andto expose said working surface portion to the pressure of fluid in saidreservoir.

7. A fluid motor for operating a circuit breaker comprising casingstructure, a piston movable within said casing structure, said piston.having a first wall portion cooperating with said casing structure todefine a reservoir filled with high pressure fluid, said first wallportion forming a pressure-confining wall of said reservoir,

a seat against which said piston abuts so as to seal ()ff' a secondportion of its surface from the high pressure fluid in said reservoir,structure defining. a pilot chamber communicating with said sealed-oil.second portion, and pilot valve means movable to control: the fluidpressure within said pilot chamber.

8. A fluid motor comprising casing structure, a piston movable withinsaid casing structure, said piston having a first Wall portion.cooperating. with said casing structure to define a reservoir filledwith high pressure fluid, said first wall portion forming apressure-confining wall of said reservoir, a seat against which saidpiston abuts so as to seal off a second portion of its surface from saidhigh pressure fluid, structure defining a pilot chamber communicatingwith said second portion, pilot valve means disposed between saidreservoir and said. pilot chamber and movable to permit high pressureg"s to flow from said reservoir into said pilot chamber whereby toinitiate withdrawal of said piston from its seat.

9'. A fluid motor comprising casing structure defining a chamber filledwith high pressure fluid, a walled piston movable in said chamber,sealing means on the casing structure and engageable' with said pistonto seal off a portion of the piston wall fromv the high pressure fluidin said chamber, control means. including a pilot valve movable to applyhigh pressure fluid to said pistonwall portionv wherebyto initiatemovement of said piston out of engagement with said sealing means so:that high pressure. fluid from said reservoir flows: past the sealingmeans and into driving relation with said piston wall portion, and.means for maintaining said chamber substantially closed. against theexit of high pressure fluid for a predetermined period of time aftermovement of said piston is initiated.

1 0. A fluidv motor comprising enclosing structure defining a reservoirfilled with high pressure fluid, said enclosing structure comprising amovable piston having a working surface, means urging said piston to aposition rhere at least a portion of its working surface is eflectivelysealed ofl from the high pressure fluid in said reservoir, control meansfor initiating movement of said piston comprising structure defining apilot chamber communicating with said sealed-oil portion of said workingsurface, and pilot valve means for controlling the fluid pressure withinsaid pilot chamber.

11'. A fluid motor comprising enclosing structure defining a reservoirfilledwith high pressure fluid, said enclosing structure comprising amovable piston having a working surface, means urging said piston to aposition where at least a portion of its working surface is effectivelysealed off from the high pressure fluid in said reservoir, control meansfor initiating movement of said piston comprising structure defining apilot chamber communicating with said sealed-off portion of said workingsurface, and pilot valve means disposed between said reservoir and saidpilot chamber and operable to control the fluid pressure within saidpilot chamber;

12; A fluid motor comprising casing structure, a piston movably mountedWithin said casing structure, said piston having a wall cooperating withsaid casing structure to define a reservoir extending about said pistonand filled with fluid under high pressure, said piston wall iorming apressure confining wall of said reservoir, a seat for said piston, meansurging said piston against said seat so as to seal off a portion of saidpiston wall from said high pressure fluid, control means for initiatingmovement of said piston away from said seat, said control meanscomprising a pilot chamber communicating with said sealed-oil? portion,and pilot valve means arranged to control fluid flow into said pilotchamber.

13. In a circuit breaker having a movable contact member, a fluid motorhaving a contact actuating piston, operating mechanism coupling saidpiston to said movable contact member, said fluid motor comprisingcasing structure, a piston movable within said casing structure, saidpiston having a first wall portion cooperating with said casingstructure to define a reservoir filled with high pressure fluid, saidfirst wall portion forming a pressureconfining wall of said reservoir,sealing means engageable with said piston in its initial position toseal off a second portion of the piston Wall from said high pressurefluid, control means for initiating movement of said piston out ofsealing engagement with said sealing means, said operating mechanismbeing provided with lost motion therein which permits said control meansto effect said initial piston movement independently of movement of saidcontact member.

14. A circuit breaker comprising relatively movable contacts, a fluidmotor for effecting relative movement of said contacts, anormally-closed pilot valve openable to initiate operation of said fluidmotor, said pilot valve being disposed in a reservoir containing highpressure fl'uid, said valve when closed having a greater area exposed tofluid pressure acting in a closing direction than is exposed to fluidpressure acting in an opening direction whereby said high pressure fluidnormally urges the valve toward closed position with a force varyingwith its pressure, biasing means urging said valve toward open position,a magnetic latching device comprising a magnet acting to restrain saidbiasing means and to hold. said valve in closed position, said latchingdevice being responsive to predetermined electrical conditions to free.said biasing means to open said valve, spring havingsuificient strengthto overcome the combined force of said magnet and the fluid pressureforce on said valve when pressure in said reservoir falls below apredetermined level.

15. In combination, a fluid motor comprising an actuating piston and anormally-closed pilot valve openable to initiate movement of saidactuating piston, said fluid motor comprising structure defining areservoir filled with high pressure fluid, said valve being disposed insaid reservoir and, when closed, having a greater area exposed to fluidpressure acting in a closing direction than is exposed to fluid pressureacting in an opening direction whereby said high pressure fluid normallyurges said valve toward closed position with a force which is a functionof said pressure, biasing means opposing said force and urging saidvalve toward open position, said biasing means being arranged to opensaid pilot valve when pressure in said reservoir falls below apredetermined level.

16. A circuit breaker comprising separable contacts, means biasing saidcontacts toward closed position, fluid motor means operative to separatesaid contacts, a valve openable to initiate operation of said motormeans, means for resetting said valve to its closed position afteroperation of said motor means has been initiated, restraining means forholding said contacts in open position against said biasing means,actuating means for disabling said restraining means whereby to permitsaid biasing means to close said contacts, interlock means operativelyinterconnecting said valve and said actuating means, said interlockmeans normally being responsive to movement of said valve to render saidactuating means inoperative to disable said restraining means wheneversaid valve is open, whereby the biasing means can move the contacts toclosed position only when said valve has been reset to its closedposition.

References Cited in the file of this patent UNITED STATES PATENTSHouplain June 28, 1932 Ray Mar. 27, 1945 Paterson May 20, 1952

